A substantial number of aqueous and gaseous streams contain organic and/or metallic contaminants which must be removed to meet governmental laws and regulations. Non-limiting examples of contaminated aqueous streams include: those emanating from municipal water supplies; those waste water streams resulting from various pharmaceutical, chemical, petrochemical, and refining processes; and, those resulting from various other industries such as the pulp and paper industry. Contaminated ground water streams must also be treated depending on their intended use. Contaminated gaseous streams can contain organic contaminants and/or metal contaminants in the form of metal vapors or vapors of compounds that contain one or more metals.
One type of aqueous stream which has proven difficult to treat in a cost effective manner is an aqueous stream containing relatively low levels of organic components, typically volatile organic components. Such streams are often found in petroleum refineries and chemical plants wherein water is often initially present, or subsequently found in processes for producing various organic chemicals and products therefrom. Metallic contaminants, such as mercury, lead, copper, zinc, and cadmium are also often found in such streams.
Various conventional techniques have been developed for removing such contaminants from aqueous streams, particularly when the contaminants are organic constituents. One such technique involves air stripping. Air stripping techniques typically involve the use of packed, or bubble tray, columns wherein the contaminated aqueous stream is passed counter-current to a flow of air. Organic contaminants pass from the aqueous liquid phase to the gaseous phase owing to the difference in concentration of organics in the two phases. That is, the organic constituents pass from the more concentrated aqueous phase to the less concentrated gaseous phase. The stripped organics are eventually released to the atmosphere with vented air. This of course creates a problem with respect to the release of such contaminants into the environment as air borne contaminants. The instant invention can be used to remove contaminants from both the aqueous and the gaseous phases.
Another conventional technique consists of bubbling air directly into the contaminated aqueous stream by use of diffusers or bubblers. Such a technique has the disadvantage of being able to remove only trace amounts of organics, typically less than about 10 wppm. A source of compressed air is also needed, thereby increasing the capital investment and operating costs for such a technique.
One leading commercial technique for removing organic and metallic contaminants from both aqueous and gaseous streams is adsorption onto a solid adsorbent material, such as activated carbon, preferably oxidized activated carbon. For example, U.S. Pat. No. 5,021,164 teaches a process wherein oxidized activated carbon containing relatively low levels of acidic oxides per unit of carbon is used to remove organic contaminants from an aqueous stream. One disadvantage with the use of conventional activated carbon in aqueous systems is that it quickly becomes saturated with water molecules thereby reducing the available volume for adsorption of undesirable organic molecules.
Consequently, there still remains a substantial need in the art for more efficient and effective processes for removing contaminants from aqueous streams.